Using different timesteps for features and target value
I don't know what kind of price data you're dealing with. I suppose the order of the data matters a lot, so my suggestion would be:


Use LSTM as it handles time series better
You can predict 3 consecutive numbers from an RNN as the next three days' predictions
Try regression first, it is likely it will not work (or just flatten the curves, depend on your data noise), then classification is an easier approach
Don't forget normalization